Loader vehicles are generally exposed to serious stress and strain in its operating environment. Especially vehicles operating in mines; running 24-hours in a rough and dangerous environment, need to be equipped with powerful, durable and secure constructions of simple mechanical details. The more complicated construction, the larger risk for operational stoppage. Loaders and trucks used to remove masses of rock from mines generally have a load capacity of 1-20 tons and 20-50 tons respectively. Thus, the mining environment make great demands on the vehicles, both constructional, ergonomic and safety demands.
For different kinds of loaders for moving of material, such as mining loaders and other front end loaders, it is sometimes desirable to safely prevent the boom from unintentionally lowering from an elevated position, as an example when an driver needs to perform some kind of service or maintenance beneath the boom arm. The boom arms with its bucket (sometimes with load) must be raised and kept in an elevated position, to facilitate such service to be effected. Thus, the elevated boom with its bucket presents a dangerous hazard for the driver while carrying out the service. Different kinds of arrangements for preventing the boom from lowering beneath a certain level or to retain them in a certain position have therefore been used within the field.
Some of the known arrangements acts on the boom cylinder, preventing it from retracting. Another known conventional arrangement of preventing the boom from lowering beneath a certain position is to insert a steel bar or wood log transversally between the boom and the boom cylinder or part of the vehicle/carrier. It is easily understood that this bar or log has to be of considerable dimension to withstand the stress from the boom and bucket—especially for mining loaders. Sometimes even two persons are required to put the bar/log in place. It is also easily understood that the positioning of the bar/log and subsequent lowering of the boom is dangerous, since the bar/log may move under the stress from the boom causing the boom to lower abruptly.
U.S. Pat. No. 4,355,944 discloses an arrangement on a front end loader with a lock pin being manually inserted in apertures arranged in supports on the vehicle frame. The lock pin can be secured in the aperture by way of a retainer pin. The retainer pin is also used to keep the lock pin in a storage bracket. This arrangement involves manually lifting of the pin from its storage to its locking position and contains several small parts, which makes the arrangement both heavy to handle for the driver (it may be difficult to lift a heavy pin and fit it into the aperture) as well as delicate—not suitable for a rough environment.
U.S. Pat. No. 3,730,362 discloses a skid steer loader provided with a locking mechanism, comprising a rather complicated link mechanism for movement of a pair of pins. Such link mechanism, adapted for a small skid steer loader, will not be suitable for a loader in rough and dirty environments such as mines.
The problem with known locking arrangements is that they are not secure enough for the driver, heavy to handle and/or not suitable for heavy loaders in a rough environment.